Unstable plaque is well established as producing high risk for sudden myocardial infarction (MI), through plaque rupture and subsequent thrombotic response, or thrombosis generated at the inflamed plaque surface. It cannot be located by angiography, and has been estimated to account for 60-70 percent of fatal MIs and up to 85 percent of all MIs. Accumed Systems, Inc. will develop a Thermal Sensing Catheter (TSC) to identify unstable plaque. Such measurements have been made in research labs, but no such product now exists. Technological innovation to achieve this includes developing new micro-thermistor and specialized manufacturing techniques to embed them in sensing arms, as well as developing new and novel testing techniques. It will measure the surface temperature of the inner wall of coronary arteries at multiple sites and identify sites of unstable plaque. Specific aims: 1) Prove the viability of intra-arterial measurements by making repeated measurements of simulated hot spots in canine arteries with prototype catheters. Demonstrate meeting preliminary spatial, thermal, and temporal specifications. 2) Confirm the functionality of the design and generate prototypes for the next round of tests on atherosclerotic rabbits to take place in Phase II. PROPOSED COMMERCIAL APPLICATION: The Thermal Sensing Catheter (TSC) to be developed will have immediate commercial applications in the large (est. $200 million/year) market for atherosclerotic plaque stability assessment. The underlying technology will also have a wide range of other cardiovascular applications where inflammation is present, e.g. myocarditis, valvulitis, aortis, as well as in those in other areas about to be biopsied, such as skin lesions, gingival lesions and urinary bladder.